Illegal immigration into the United States is massive in scale. The growing number of illegal aliens is a sign of how dangerously open the US borders are. The presence of millions of undocumented migrants distorts the law, distracts resources, and can effectively create a cover for terrorists and criminals. Immigrants can be classified as illegal for one of three reasons: entering without authorization or inspection, staying beyond the authorized period after legal entry, or violating the terms of legal entry. The consequences of illegally entering the US provides for a fine, imprisonment, or both for any immigrant. Stricter enforcement of the border in cities has failed to significantly curb illegal immigration. Once undocumented migrants enter the US, they can easily blend in with legal US citizens.